1. Field of the Invention
This invention relates to an ink removal method for a rotary offset press, etc.
2. Description of the Related Art
In a lithographic press such as a rotary offset press, an image is formed on a surface of a plate mounted on a plate cylinder by ink and water supplied by an inking device and a dampening unit, respectively. This image is transferred to paper directly or via a blanket cylinder, whereby printing is performed. The inking device is generally designed to transfer ink, stored in an ink fountain, from an ink fountain roller to an ink ductor roller, an ink distribution roller, an ink oscillating roller, and ink form rollers in this order, thereby supplying ink to the plate surface. On the other hand, the dampening unit has a water pan storing water, a water fountain roller rotating while being immersed in the water in the water pan, a dampening form roller rotating with its circumferential surface in contact with the plate surface, and a ductor roller (metering roller) disposed between the water fountain roller and the dampening form roller, and having a circumferential surface in contact with both of these rollers. Water taken up by the water fountain roller is continuously transferred to the dampening form roller via the ductor roller, and fed to the plate surface.
As printing proceeds in the above-described lithographic press, the phenomenon that ink emulsified upon supply of water from the dampening unit clings to the dampening form roller occurs. If this phenomenon progresses, the supply of water from the dampening unit is not performed smoothly and causes smudging of a print, such as scumming or tinting. Thus, it is necessary to remove ink from the dampening form roller at a predetermined time.
Japanese Unexamined Patent Publication No. 1995-171943 discloses a configuration, in which a rider roller acts as a bridge between a dampening form roller and ink form rollers. This configuration can make the water film thickness of the dampening form roller constant, thereby preventing ink from clinging to the dampening form roller. However, the number of rollers arranged in a small installation space increases further. Thus, this configuration cannot be applied widely to lithographic presses, and lacks general purpose properties.